Way back in the summer of 2013, Elon Musk showed off a new piece of tech that could swap the battery of a Tesla Model S in 90 seconds. In one simple move, these battery swap machines made electric cars almost as convenient as their petrol- and diesel-powered brethren.

The original plan was to roll out the tech to Supercharger stations in the second half of 2013, but they never emerged. Now, a single Supercharger station in Harris Ranch California has been equipped with the battery swap tech, and Tesla has started inviting some Model S owners to come try it out.

The idea of Battery Swap (yes, that’s its official name) is to provide a faster but more expensive option for Model S owners in need of a quick recharge. As it stands, Tesla owners can rock up to any Supercharger and get a free charge — but it takes 75 minutes to recharge the battery completely (or about 30 minutes for a half-charge). This is fine if you’re stopping for lunch, or you’re in no rush to get somewhere — but obviously conventional automobiles, with their rapidly pumped hydrocarbon fuel available on almost every street corner, have a sizable advantage when it comes to refilling.

Battery Swap was intended to bridge this gap between electric and conventional vehicles. You roll up to a Supercharging station in your Model S, maneuver your car over the special Battery Swap gizmo, and then wait while it unbolts your battery and swaps in a new one. Back in June 2013, Musk showed a Battery Swap that took just 90 seconds — while it took a full three minutes for an Audi to fill its tanks with gas. While conventional Supercharging is free, Tesla estimated a cost of around $60 to $80 for a Battery Swap (i.e. about the same price as filling up with gas). In theory, you would then return at some later date to pick up your original battery pack, or have your original battery pack delivered to your home (this part of the process isn’t fully fleshed out yet).

Anyway, Tesla wanted to roll out Battery Swap to its Supercharger stations in late 2013 — but for some reason it never happened. Judging by the Tesla blog post announcing the start of the Battery Swap Pilot Program, it sounds like the delays might have been due to the additional titanium and aluminium shielding that was added to the Model S following a couple of battery fires. The shielding has to be removed before the battery can be swapped out, and obviously that required some changes to the machinery. Due to these additional steps, the battery swap now takes “approximately three minutes” (so, the same as the gas-powered Audi!), but Tesla is “confident that the swap time could be reduced to less than one minute” in the future.

To begin with, Battery Swap is only available by appointment, “across the street from the Tesla Superchargers at Harris Ranch, California.” It sounds like Tesla is asking Model S owners to come on down and try out the battery swap — so it’s more of an early alpha test, rather than a full-blown beta test where a few Model S drivers are using Battery Swap on a daily basis. Given the value of a Model S battery pack ($10,000+), and the potential logistics nightmare of tracking who owns which battery pack (and then shipping them around the country), I suspect it’ll be a while before we see a full-scale roll-out of Battery Swap.

In an ideal world, Battery Swap would be rolled into the cost of a Tesla car — rather than owning the battery pack that’s attached to your car, Tesla would instead permanently loan out battery packs. Each Supercharger station would just slot in the best battery pack that it currently has available, and retire (or recondition) battery packs when their range drops below a certain threshold. Tesla would need lots of batteries to make it work, of course — especially once the mass-market Model 3 arrives — but that’s what the Gigafactory is for!